Time domain reflectometry has been previously known effective in methods for determining the level of a liquid, such as in a tank. In such time domain reflectometry methods, electrical pulses are conveyed along a transmission line to an electrically conductive probe extending over the range of liquid levels being detected. The stimulating electrical pulses produced in the time domain reflectometry system are partially reflected at the vapor-liquid interface due to a change in the electrical impedance. The impedance change is associated with the differences in the dielectric strength between the liquid and the overlying gas or vapor. The electrical permittivity is another term indicating the dielectric properties of the fluids involved.
U.S. Pat. No. 4,786,857 to Charles L. Mohr et al., entitled "Methods and Apparatus for Time Domain Reflectometry Determination of Relative Proportion, Fluid Inventory and Turbulence," disclosed apparatus and methods for using time domain reflectometry to determine the relative proportions of intermixed constituents in a fluid system. Such apparatus and methods can be used to determine the relative proportions of liquid and vapor even when the liquid and vapor are intermixed either homogeneously or non-homogeneously. Measurement capabilities such as these are particularly valuable to the process industries and nuclear energy production. The systems can be used to monitor nuclear reactor coolant systems, in which the total inventory of system coolant, including intermixed water and steam, must be determined under a variety of conditions, including even accident conditions. Methods are also described for obtaining indications of turbulence in fluid mixtures by measuring variations in fluid properties over time.
The Mohr patent mentioned above disclosed a probe including a inner centrally located electrode mounted within a cylindrical outer electrode. The cylindrical outer electrode was provided with slots to allow fluid to pass into the annular volume between the inner and outer electrodes. The probe was immersed in the mixed-constituent system. The average permittivity experienced by the electrical pulse transitting the probe was determined using time domain reflectometry. The measured permittivity was then correlated with known characteristic data of the constituents being measured to determine their relative proportions.
The probe shown in the Mohr patent was found ineffective when used in some applications. In particular, solutions rich in minerals such as from earth wells were not capable of measurement. Accordingly, there was a need for an improved probe which could be used for a greater variety of applications and still provide measurements. The current invention addresses this need for improved time domain reflectometry probes which are capable of service under a variety of conditions with accuracy and reliability.